Programmable highly temperature and supply independent oscillator

Abstract

An oscillator circuit generates an output frequency that is substantially independent of power supply and temperature variations. The oscillator circuit can be implemented using conventional complementary metal-oxide-semiconductor technology. The oscillator circuit is suitable for use as an internal oscillator for generating a stable reference frequency in telecommunication receiver modules.

Description

BACKGROUND OF THE INVENTIONThe present invention relates in general to integrated circuits, and in particular to a robust oscillator circuit that is insensitive to variations in temperature and power supply voltage level.In various types of telecommunication systems a reference frequency is commonly used as an acquisition aid in the receiver module. In those applications, such as ATM and SONET, that require reference frequencies of 35 Mhz or higher, generating a stable reference signal at such high references places a high cost and size burden on the sub-system or module. Crystal oscillators or tank circuits that are commonly used to generate the reference frequency take up additional board space and can be expensive. Thus, a receiver that does not require an externally generated reference frequency is very desirable. Internally generated reference frequencies, however, tend to be less accurate than their external counterparts. This is because on-chip oscillator circuitry is more su...

AI Technical Summary

Benefits of technology

The present invention provides a fully integrated, temperature and supply independent oscillator circuit that provides a stable and accurate reference frequency. Broadly, the circuit of the present invention uses a relaxation type oscillator that operates by supplying a charge current to a capacitor that is charged and discharged based on the level of a threshold voltage. The invention further includes circuitry that generates the charge current and the threshold voltage such that the temperature dependent parameters in the charging current substantially cancel those in the threshold voltage, thereby yielding a substantially temperature independent output frequency. In one embodiment, the oscillator circuit is made digitally programmable so it can generate different frequencies required for different circuit applications. The oscillator circuit of the present invention can be implemented using conventional CMOS technology.

Problems solved by technology

In those applications, such as ATM and SONET, that require reference frequencies of 35 Mhz or higher, generating a stable reference signal at such high references places a high cost and size burden on the sub-system or module.

Crystal oscillators or tank circuits that are commonly used to generate the reference frequency take up additional board space and can be expensive.

Internally generated reference frequencies, however, tend to be less accurate than their external counterparts.

This is because on-chip oscillator circuitry is more susceptible to variations in temperature and power supply voltage.

However, most require complex circuitry often relying on the temperature behavior of bipolar transistors.

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